Quaternion Signal Processing for Nonlinear Ultrasonics

Localization and classification of scattered nonlinear ultrasonic signatures in complex damaged media using time reversal approach has been studied. We suggest analyzing ultrasonic experimental data with the use of quaternion signal processing. Starting from the basic concepts of Pulse Inversion mode for nonlinear ultrasonics signal processing, a 4-dimensional quaternionic extension is suggested in order to extract nonlinear signatures of wire arc additive manufacturing samples. For the proof of concept of this new signal processing method, experiments were conducted using various chirp-coded frequency sweep excitations in the 200kHz-800kHz bandwidth. Several experimental configurations were proposed on each sample: the use of a 1 MHz 16-elements Nondestructive Testing probe where each element was isolated and used as a single receiver. For each excitation on a single element, several symmetrized amplitudes of excitation are proposed in connection with quaternion properties and in order to activate several orders of nonlinear signatures. The basic scheme and some preliminary experimental results are presented and induce the definition of the new quaternion excitation symmetry analysis method.